Does your project involve fish passage? Here’s what you need to know:

The New Zealand Government recently introduced regulations on fish passage into the updated National Policy Statement for Freshwater Management (NPS-FM) and National Environmental Standard for Freshwater (NES-F).

Many of New Zealand’s native freshwater fish species are diadromous, meaning they must migrate between freshwater and marine habitats to complete their lifecycles. Whether it’s our breeding population of eels leaving New Zealand’s freshwater habitats to spawn in warmer Pacific waters, or whitebait (the juvenile stages of five galaxiid species) swimming back into river and streams after spending a few months out at sea, the migratory stages are critical. Structures such as culverts for road crossings, along with dams, weirs, fords and tide gates, can delay or prevent fish movement and stop them from accessing these critical habitats.

The New Zealand Government recently introduced regulations on fish passage into the updated National Policy Statement for Freshwater Management (NPS-FM) and National Environmental Standard for Freshwater (NES-F). These new regulations aim to prevent the continuation of physical barriers reducing habitat connectivity for migrating fish. The NPS-FM outlines policies with the purpose of, amongst other things, dealing with new structures (or the alteration of an existing structure) within streams and rivers to ensure these structures are “fish friendly”.

Essentially, the NPS-F requires any new structures within waterways (or alteration of existing structures) to maintain or improve fish passage; unless there is a need to exclude certain fish species in order to protect desired fish species, those species’ life stages or a certain habitat. The NPS-FM provides direction to the NES-F, which prescribes rules and regulations to meet those policies and is issued under the Resource Management Act (1991).

Regarding fish passage, the NES-F identifies requirements and activity statuses specifically for culverts, weirs, flap gates, dams and fords. For example, as a permitted activity, culverts are fundamentally required to provide for the same passage of fish upstream and downstream as would exist without the culvert (except during associated works). And there are numerous conditions, including design and monitoring requirements, for the installation to be a permitted activity.

There are numerous aspects that need to be considered when designing a new structure for streams, and for culverts these include:

  • Slope of the culvert,
  • Water velocity,
  • Culvert width,
  • Type of culvert (box, open bottom, etc),
  • Imbedded depth,
  • Bed substrate, and
  • Continuity of geomorphic processes (i.e. movement of sand and debris).

Generally, new culverts will need to be much larger than engineering/ hydraulic requirements and meet minimum standards listed in the NES-F, including e the design elements listed above. The monitoring that is also required needs to be undertaken before and after the culvert is installed to ensure fish passage is maintained for the life of the structure. It’s likely that this will result in increased “whole of life” costs for culverts and raises the question of whether a bridge is the more practicable and cost-effective (not to mention, ecologically better) option.

In some instances, it can be difficult to achieve ideal fish passage scenarios, particularly if there are conflicting goals, but it is clear now that fish passage is a principal outcome requirement. Where permitted activity rules, as now clearly detailed in the NES-F, cannot be met, a resource consent will be required.

Boffa Miskell’s ecologists are known for thinking outside of the box (culvert) and coming up with ideas to create innovative solutions and positive environmental outcomes. If your project involves fish passage, or you have questions about how these policies may affect you and your business, get in touch with one of our ecologists in an office nearest to you.

For further information please contact Dr. Tanya Blakely, Kieran Miller, Dr Ian Boothroyd or Dr. Vaughan Keesing

5 February 2021